Dark mode in a viewer, or dark mode in the file
Many PDF readers can show a document in dark colors, but only in that reader, on that device, and not every reader has the option. Making the file itself dark means it opens that way everywhere: on a phone, on a tablet in bed or on a laptop late at night, with no setting to find first.
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Which tool you need
Reading in bed or through a long evening
Choose Dim. Light gray on dark gray has less contrast than pure white on black, which many people find easier over a long stretch.
A phone with an OLED screen, or a dark room
Choose Black. The background is fully dark, which an OLED screen shows by switching those pixels off.
A document full of photos or diagrams
Leave Keep photos and pictures as they are turned on, so they come back to their own colors instead of looking like negatives.
The document has to be printed as well
Print the original, not the dark copy, which would use a great deal of ink. For a cheaper print, PDF to Black and White is the better tool.
How a page turns dark and keeps its text
Redrawing every page as a dark picture would be simple, and it would end text search, copying and links. Instead each page gets a filter, stored in the file, that inverts what lies beneath it: white paper becomes black and black text white, while the text itself is untouched.
Inverting also turns photos into negatives, so pictures are inverted first and the filter inverts them a second time, which brings them back to their own colors. Formats that cannot be prepared this way are left alone, come out as negatives, and are counted in the result.
Colors that change, and colors that stay
Everything drawn on the page turns to its opposite color. With Black, red text comes out cyan, blue text comes out yellow, and a yellow highlight that was flattened into the page turns blue.
Comments are drawn above the filter instead, so a highlight that is still a comment stays yellow on the dark page, and a form field stays white.
What Dim costs a picture
Kept pictures are not saved again: each is marked to be drawn inverted, and the filter turns it back. Under Black that returns the picture exactly; under Dim the filter is light gray rather than white, so a picture's darkest tones come out a little flatter.
The preview inverts photos along with the page. With Keep photos and pictures as they are on, a photo that looks like a negative there still comes out in its own colors in the PDF.
What to know before you start
- Comments, highlights and form fields stay light.
- Colored text and charts swap to their opposite colors.
- Some pictures, CMYK and JPEG 2000 among them, come out as negatives.
- A password-protected PDF has to be unlocked before it can be turned dark.